I check the pressure once in two week. I have seen that the pressure goes down by 2-3 psi in some of my tyres in those 15 days. I inflate the tyres upto 32 psi for the front tyres and 30 psi for the rear on my alto as recommended by by servicing garage.
I check tyre pressure every 15-20 days. Sometimes, it stretches to a month. I normally fill petrol from Reliance pump which is nearest to my home. Unfortunately, air filling / pressure checking arrangement is not available there. I go to a tyre repair shop in the vicinity for checking tyre pressure. They have an analogue pressure gauge which doesn't give accurate readings and they mostly end up filling at least 4-5 psi more than recommended values.
I have purchased a digital tyre gauge and check tyre pressure early next morning and reduce the pressure to recommended values.